Charles Ellicott Commentary Isaiah 14:30

"And the first-born of the poor shall feed, and the needy shall lie down in safety; and I will kill thy root with famine, and thy remnant shall be slain." — Isaiah 14:30 (ASV)

And the firstborn of the poor shall feed. — As the children of the needy in Psalms 72:4 are simply the poor as a class, so the “firstborn” are those who, as it were, inherit the double portion, not of riches, but of poverty. (Compare to the firstborn of death in Job 18:13.) The people spoken of are those of Judah, which in the days of Ahaz had been brought very low (2 Chronicles 28:19).

For these the prophet foretells a time of plenty; not so for Philistia. Either through the sieges of their towns or the devastation of their fields, they would be reduced to the last extremities of famine. With them there should be no “remnant” to return.